The invention relates generally to chemical compositions, and more specifically to chemical compositions and methods for stripping coatings from metal articles.
Traditionally, metal articles, including operative parts as well as tooling, are stripped, etched, and cleaned with a standard corrosive solution consisting of an acid such as a high molarity hydrochloric acid (HCl), sulfuric (H2SO4), or nitric acid (HNO3), or mixtures thereof. Depending on the application and the coating, the acid may be supplemented with a wetting agent to dissociate the acid molecules to increase their effectiveness at removing coating or other molecules diffused into the metal substrate. The solution is otherwise substantially free of contaminants, such as iron. Once coating contamination of the solution exceeds a threshold concentration, the solution is discarded and/or recycled.
In many instances, the acid is not selective between the coating or contaminant and the metal substrate, particularly when the part has been previously run in a hot engine. The acid continues to attack the metal substrate, causing pitting or other surface damage that must be repaired. If significant, such damage can result in scrapping of the part. In addition, pure corrosive acids do not completely remove certain coatings, and the parts must be subsequently exposed to a mechanical desmutting process. Further, the stripping and desmutting process using a pure acid solution often needs to be repeated two or more times before the coating is completely removed from the substrate.